FAMILY ANATINID.E — THEACIA. 237 



Thracia CONRADI. 



PLATE XXVIII. FIG. 384. 



Thracia declivis. Conrad, Am. Marine Conch, p. 44, pi. 9, fig. 2 (exc. syn.). 



T. conradi. Couthouy, Bost. Jour. Nat. Hist. Vol. 2, p. 153, pi. 4, fig. 2. 



T. id. Rossel, Essex Jour. Nat. Hist. Vol. 1, p. 75. 



T. id. Gould, Invertebrata of Mass. p. 50. 



Description. Shell thin, fragile, ventricose, rounded in front, narrowed and subtruncate 

 behind. Beaks prominent, with one or more obtuse carinations extending to the angle of the 

 basal and posterior margins ; the beak of the right valve perforated to receive the points of 

 the other. Right valve more convex, and extending somewhat beyond the left : valves slightly 

 gaping. Hinge toothless, but represented by strong rounded eminences. Surface with a 

 thin epidermis, and with concentric undulated stria?. Palleal impression with an acute angu- 

 lar sinus : no ossiculum. 



Color. Epidermis light brown ; within white. 



Vertical axis, 2*2; transverse ditto, 2'7. Diameter, 1*4. 



This is one of the largest species of the genus, and is found along the coasts of Rhode- 

 Island, Massachusetts and Maine. Mr. I. Cozzens assures me that he has obtained it in 

 Long island sound, along the shores of Connecticut, so that in all probability it exists on the 

 shores of this State, 



(EXTRA-LIMITAL.) 



Genus Amphidesma, Lamarck. Shell inequilateral, transverse, suboval or somewhat rounded : sides 

 slightly gaping. Hinge with one or two cardinal teeth, and a narrow groove for the internal 

 ligament; external one short; internal one fixed in the internal grooves. 



A. flexuosa. (Lam. Vol. 2, p. 344. Tellina id. Montagu, Test. p. 72.) Shell suborbicular, 

 thin, convex, pellucid, fragile, with minute irregular concentric striae. A remarkable furrow 

 extends from the apex parallel to the cartilage-slope, and forms a deep curve in the margin fit its 

 termination. Hinge with an obsolete tooth. Color, white. Length, 0-6. On the authority of 

 Mr. Redfield, this has been found on the coast of Massachusetts. 



A. transversa. (Say, Conch, pi. 28.) Shell transversely short, oval, nearly equilateral, compressed, 

 a little gaping. Hinge nearly central: margins subequally rounded behind and in front; the 

 former somewhat more obtusely so. Basal margin regularly rounded without any undulation in 

 front: apex obtuse, but little prominent. Cardinal teeth two; fosset dilated, fusiform, abruptly 

 very narrow at the beaks : lateral teeth none. Posterior muscular impression very slender and 

 elono-ated. Color, tinged with yellowish. Width, 1-5. Long Island Sound? Southern Coast. 



A. ? punctata. (Sat, Ac. Sc. Vol. 2, p. 308.) Orbicular, with numerous minute concentric wrinkles 

 and very numerous minute punctures. No lateral teeth ; two primary teeth in each valve, of which 

 one has a deep groove: within, a small rim or projecting line runs near the edge from the hinge 

 to the basal margin. Color, white. Length, 0-3; width, 0-3. Southern Coast. 



A. orbiculata. (Id. lb. Vol.2, p. 317.) Shell orbicular, somewhat compressed: beaks nearly central, 

 and a little prominent ; valves slightly wrinkled transversely. Hinge with two lamellar teeth ; 



